Fault-tolerance is designed into electronic systems by providing redundant capability for critical functions. In synchronous fault-tolerant systems, redundant clock generators are often provided to enable switchover from one clock generator to another in response to a failure detection. Unfortunately, switching between clock generators is not a trivial task. Even if two clock generators are identical in design and construction, they typically generate clock signals that exhibit at least a small frequency difference and therefore drift out of phase with each other. Consequently, an abrupt transition from one clock generator to another is likely to yield a shortened high or low pulse within the clock waveform, referred to herein as a runt pulse. If short enough, the runt pulse may violate settle- and hold-time constraints of circuit elements clocked by the clock signal, resulting in improper circuit operation and ultimately to the type of system failure sought to be avoided by the redundant clock generator in the first place.